The Equal Earth Map Projection

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Map projections in 2D have been a long-standing problem for cartographers. The problem has traditionally been to accurately portray size of land masses and show them in a way that does not distort orientation or makes it hard to understand the map due to its odd appearance.

Offsetting Distortion of Land Masses

The Mercator projection, first appearing in 1569, which had been popular and is still commonly seen in classrooms, has been heavily criticized for its distortion of land masses and their areas, particularly near the poles (e.g,. Greenland appearing far larger than it actually is). One popular response was the Gall-Peters projection, which accurately shows the size of regions but heavily distorts their appearance so that the projection could properly display size. In fact, claims that were made about this projection, such as “absolute angle conformality”, “no extreme distortions of form”, and “totally distance-factual,” have all been refuted by cartographers.[1]

Mercator map projection overlaid with Tissot's indicatrices showing a greater distortion of land sizes at higher latitudes. Map: Flex Projector

Mercator map projection overlaid with Tissot’s indicatrices showing a greater distortion of land sizes at higher latitudes. Map: Flex Projector

Other Equal Area Map Projections

The Gall-Peters projection is not the only equal area projection. The Sinusoidal projection, for instance, provides an equal area projection. However, like the Gall-Peters projection, the appearance is heavily distorted to make way for accurate area, which makes it distorting for the viewer to look at since the expectation of a cylindrical form is not met. This also means it is hard to get a sense of distance between locations and where in the globe regions would be accurately located, as the meridians and parallels are heavily distorted. This distortion has made the Sinusoidal and related types of projections minimally used in secondary and higher education.[2]

Gall-Peters map projection with Tissot's indicatrices. Map: Flex Projector

Gall-Peters map projection with Tissot’s indicatrices. Map: Flex Projector

Development of the Earth Earth Map Projection

Recently, Boston schools had announced the use of Gall-Peters projection as their new type of map projection for their maps. However, given the problem of Gall-Peters, researchers began to look for new ways tomake a projection sensible for area, navigation, and appearance. This led to the development of the Equal Earth map projection, which has quickly gained influence due to its ability in maintaining accurate area without distortion.[3]

Robinson map projection with Tissot's indicatrices. Map: Flex Projector

Robinson map projection with Tissot’s indicatrices. Map: Flex Projector

The Robinson projection, used by Šavrič et al. (2018) in their work as a starting point, is the most similar to Equal Earth projection in that this projection also does not distort in a significant way the appearance of the world. The main problem, however, is that to balance appearance and size, the Robinson projection gives away some accuracy in appearance and size to make it a compromising approach relative to projections that focus on appearance or area only. The meridians curve gently and distortions are limited, mostly along the poles. Nevertheless, inaccuracies in area mean that different regions are not representative to their true appearance. But, because the projection balances such inaccuracies to keep them at a minimum, it does serve as a starting point where one can try to fit area to be accurately shown while maintaining the shape of the projection so that continents and areas are not distorted in appearance. On the other hand, the Equal Earth projection, while appearing very similar to Robinson, improves on its weaknesses. Mainly, area is accurately shown while also keeping a pleasing way in which the projection is shown, that is it also minimizes distortion. Thus, it is arguably the first projection to accurately show area in a way that many can easily visually perceive and understand similar to the Robinson projection.

Equal Earth map projection with Tissot's indicatrices. Map: Flex Projector

Equal Earth map projection with Tissot’s indicatrices. Map: Flex Projector

The Equal Earth projection uses four conditions that allow it to develop a way in which projection can be calculated. The first condition is there must be equal area. The second is that it is a pseudocylindrical projection, meaning that the parallels are unequally spaced. Meridians are equally spaced along the parallels. Finally, there is bilateral symmetry to maintain a x- and y-axis appearance similar to the Robinson projection. In effect, area is accurate while appearance is balanced to minimize distortions.

While some distortion is inevitable, these are very minimal in the Equal Earth projection. Overall, one can use area accurately and not feel the appearance is highly distorted. This makes it perhaps the best projection currently available that balances requirements for viewer expectation and making no area distortions.

Equal Earth map projection with a natural earth shading. Map: Strebe, CC BY-SA 4.0

Equal Earth map projection with a natural earth shading. Map: Strebe, CC BY-SA 4.0

References

[1]    For more on the problematic nature of popular projections previously used, see:  Pearson, F. (1990). Map projections: theory and applications. Boca Raton, Fla: CRC Press.

[2]    For more on the Sinusoidal projection and comparison to other projections, see:  Tobler, W. R. (1986). Measuring the Similarity of Map Projections. The American Cartographer, 13(2), 135–139. https://doi.org/10.1559/152304086783900103.

[3]    For more on the Equal Earth projection, see:  Šavrič,B., Patterson, T., & Jenny, B. (2018). The Equal Earth map projection. International Journal of Geographical Information Science, 1–12. https://doi.org/10.1080/13658816.2018.1504949.

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